One conventionally known self-cooling motor with a self-cooling fan is disclosed in Japanese Patent Application Laid-open No. 9-65632. FIG. 6 illustrates the construction of the conventional motor with a self-cooling fan. Referring to FIG. 6, a housing 1 retains bearings 2 and 3. A plate 4 retains a printed board 5 and holds the housing 1 by clamping. A core 6 has a winding wire 8 wound thereon via an insulating layer 7 so as to compose a stator. A screw 9 extends through the core 6 to be tightened to the housing 1, thereby pressing the stator against the housing 1 in a fixed relation. A rotor shaft 10 has a rotor frame 11 press-fitted thereon in a fixed relation, the rotor frame 11 adherently retaining a magnet arranged along a periphery of the core 6 via a gap. The rotor shaft 10 is press-fitted in inner rings of the bearings 2 and 3, outer rings of which are retained by the housing 1. An electronic component 12 is fixed to a radiator plate 14 by means of a screw 13 so as to be jointly mounted to the printed board 5. A self-cooling fan 15 has a larger outside diameter than the rotor frame 11 and is fixed to the rotor shaft 10.
In a brushless motor of the aforementioned construction, the winding wire produces heat in proportion to the amount of current flowing therethrough but the heat-producing winding wire is cooled by cooling air from the self-cooling fan unitarily rotating with the rotor shaft, via the plate, housing, core and insulating layer. Thus, the temperature is prevented from rising.
Because of the arrangement wherein the self-cooling fan 15 has the larger outside diameter than the rotor frame 11, and opposes the electronic component 12 and radiator plate 14 disposed on the periphery of the rotor, the electronic component and radiator plate may be located in a passage of a direct air flow from the fan. This provides a notable cooling effect on the electronic component and radiator plate.
In the conventional construction, however, the air flow from the self-cooling fan runs axially of the rotor. For effective cooling of the electronic component or the radiator attached with the electronic component, the outside diameter of the self-cooling fan needs be larger than that of the rotor. In addition, the self-cooling fan needs be spaced from the rotor to define a gap therebetween and the electronic component or the radiator attached with the electronic component needs be disposed at a place opposing the self-cooling fan. This poses a problem that the motor increases in size and the position of the electronic component or the radiator attached with the electronic component is restricted.